#include <iostream>
#include <chrono>
using namespace std;
class Person
{
public:
    Person() { ++_count; }

protected:
    string _name; // 姓名
private:
    static int _count; // 统计人的个数。
};
int Person ::_count = 0;
class Student : public Person
{
protected:
    int _stuNum; // 学号
};
class Graduate : public Student
{
protected:
    string _seminarCourse; // 研究科目
};
// void TestPerson()
// {
//     Student s1;
//     Student s2;
//     Student s3;
//     Graduate s4;
//     cout << " 人数 :" << Person ::_count << endl;
//     Student ::_count = 0;
//     cout << " 人数 :" << Person ::_count << endl;
// }
int main()
{
    Person p1;
    Person p2;
    Person p3;

    cout << Person::_count << endl;
    return 0;
}